Wichit Sirichote, wichit.sirichote@gmail.com
Build your own the CDP1802 Microprocessor training kit in the year 2018!
I designed this kit from the suggestion by Leonard Rose. The CDP1802 Microprocessor is very interesting CPU. I use the same platform as the 6809 kit. I spent a month to develop it. The first try PCB was working very good. So most of the time are spent on monitor program coding. The outlook is shown below. The kit runs with Xtal 3.6864MHz using the on chip oscillator. Memory spaces are 28kB monitor ROM, 32kB RAM and 4kB memory mapped I/O. The kit provides 36 keys, 6-digit seven segment display, 9600 UART chip, the 8-bit gpio1 debugging LED, and the text LCD interface. In addition, the 10ms tick generator is also provided for timer interrupt testing. We can enter 1802 instructions with hex code and test run directly. The built-in BREAK subroutine provides CPU registers saving. The expansion header provides interface signals for testing with IN and OUT instructions.
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| The CDP1802 Microprocessor kit 2018 |
Hardware descriptions:
U5 is the COSMAC CDP1802 Microprocessor. The CPU clock is generated by the on chip oscillator with external Xtal, 3.6864MHz. The clock signal is also supplied to the tick generator and UART chips. CLEAR pin is used for startup reset by R5-C4 time constant. WAIT signal is pulled up to logic HIGH. On power up, the CPU will start running the monitor program in ROM.
External memory is interfaced with data bus BUS0-BUS7 and A0-A15. A0-A7 emits from MA0-MA7, while the A8-A15 will need external latch, U7 and use TPA signal for latching the high address.
Memory read/write signals for EPROM, SRAM and memory mapped I/O are decoded by U4, the programmable logic device, GAL22V10. See the equations below.
U1 is 32kB EPROM, 27C256. The address space for EPROM is decoded at 0x0000-0x6FFF.
U2 is 32kB static RAM, 62256. The RAM space is located at 0x8000-0xFFFF.
All I/O are decoded to memory locations from 0x7000 to 0x7FFF.
U3, the 20-pin 89C2051 microcontroller chip produces 10ms tick. SW1 selects between 10ms tick or manual INT button.
U13, 74HC541 is 8-bit input port (PORT0). Six bits, PA0-PA5 are input signals of the row keypad. PA6 is for USER test button.
U11, 74HC573 is 8-bit output port (PORT2). The 8-bit output drives the 7-segment LED directly. No current limit resistor. U12 (PORT1) drives 6-digit common cathode pin. The brightness is controlled by software controlled PWM. PC7 is speaker output for beep signal.
U14(GPIO1), 74HC573 is 8-bit output port for 8-bit binary number display.
D14 lifts the forward biasing for proper brightness.
JR1 is 16-pin socket for text LCD interface. Any text LCD with HD44780 compatible controller can be used with no modifications. U16, HIN232 converts TTL level to RS232 level.
U15, is hardware UART using the INS8250 chips. All registers are located in memory space. The input clock signal is the same CPU frequency, 3.6864MHz. To produce 9600 bit/s, we can use internal divider with 24. It will produces 16x9600 Hz exactly.
Q2, KIA7042 is reset chip for power brownout. JP1 is 40 pins header. It is for expansion for testing the IN/OUT instructions.
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| Hardware schematic (click to enlarge) |
Hardware Features:
-CPU: Intersil CDP1802 CMOS Microprocessor @3.6864MHz clock
-Memory: 32kB SRAM, 28kB EPROM, 4kB memory mapped I/O
-Memory and I/O Decoder chip: Programmable Logic Device GAL22V10D
-Display: high brightness 6-digit 7-segment LED
-Keyboard: 36 keys
-RS232 port: INS8250 UART, 9600 bit/s 8n1
-Debugging LED: 8-bit GPIO1 LED at location $7000
-Q LED: high brightness yellow color dot LED for Q output bit
-Tick: 10ms tick produced by 89C2051 for time trigger experiment
-Text LCD interface: direct CPU bus interface text LCD
-Brownout reset: KIA7042 reset chip for power brownout reset
-Expansion header: 40-pin header
